Glossary of Audio Archiving Terms

Adapted from the National Archives: Terms Used in the Preservation of Audio, Video and Motion Picture Film. The original has been edited to include only terms that relate to magnetic audio preservation.
Reference: https://www.archives.gov/preservation/formats/glossary.html

Access Copy: Also called distribution or reference copy. An access copy should provide easy access or review of the content of a less accessible preservation or intermediate copy. The access copy is often relatively low resolution and made available online. An access copy should be a widely supported format that is easy to playback. See Additional Description and NARA’s Internal Specifications.

Acetate Magnetic Tape Base: Cellulose acetate was used as a tape substrate (base) in many early magnetic tapes from the 1940s until the mid 1960s. Acetate is susceptible to vinegar syndrome. Acetate magnetic tape bases were replaced by polyester.

Bit Rate: The amount of sample data that is collected per unit of time. This is usually expressed as ‘bits per second’ (bps) or ‘Megabits per second’ (Mbps), and is the result of sampling rate multiplied by the number of data bits per sample (or bit depth), plus any additional data such as tracking information.

Bit Depth: The number of data bits used for each individual sample. The amount of bits determines the number of discrete levels possible to place a sample within. 8-10 bit is common for video; 16-24 bit is common for audio.

Compression: Use of a method to reduce the size of digital files or streams of data, also referred to as data reduction. Compression is used to either save data storage space or better enable movement over networks or transmission lines. There are many different techniques to compress data, but all fall into one of two overall categories:

Lossless: Any data removed can be reconstructed.

Lossy: Some or all of the data removed is discarded and gone forever.

Inches per Second: Refers to the length of tape travelling past a read or write head during playback or recording. Inches per second is a valid metric for all magnetic tape and machines (both audio and video), but is normally indicated only for variable speed machines such as open reel audio. Abbreviations include ips, in/s, and in/sec. Higher speeds facilitate a broader range of frequencies able to be recorded on a tape, which generally means more fidelity.

Magnetic Media: Media in various formats that use magnetic particles to store information. When particles are read by magnetic audio or video heads, the sound and/or images that have been previously recorded will be reproduced. Some examples include: ¼-inch open reel audio, wire recordings, 1-inch video and VHS tapes. Magnetic media may contain analog or digital information dependent on the format.

Metadata: The National Information Standards Organization (NISO) defines Metadata as “…structured information that describes, explains, locates, or otherwise makes it easier to retrieve, use, or manage an information resource. Metadata is often called data about data or information about information.”

Playback Equipment: Equipment used to listen to and/or view the recorded signal of audio and video. For older formats, playback equipment may be obsolete and professional services may be needed to provide maintenance and repair.

Polyester Magnetic Tape Base: A chemically stable substrate (base) for audio and video magnetic tape. Polyester bases are durable and not susceptible to vinegar syndrome; sticky shed may still occur, but this will depend on the binder composition. Became the norm for manufacturing by the 1970s.

Preservation Copy: A preservation copy is a high quality duplicate of the original record. If the original record deteriorates beyond use the preservation copy should be able to take its place. A preservation copy should last for years or decades – at least long enough to plan for making subsequent copies once these become outdated. See Additional Description and NARA’s Internal Specifications from the U.S. National Archives and Records Administration.

Reformatting: A process in which a copy or derivative is created from the original media. This may be done for preservation or access purposes.

Resolution: The measure of how well audio, video, or film can faithfully portray images or sound. Picture cell (pixel) density and bit depth are the units of measure for individual images. Sampling rate and bit depth are the units of measure for moving images and sound.

Sampling Rate: The frequency at which information from the original recording is sampled or collected from a continuous signal. The rate is given in hertz (Hz) which equals cycles per second. One common example is the audio CD which has a sampling rate of 44,100 Hz, or 44.1 kHz.

Spoking: Condition of magnetic tape and motion picture film where excessive pressure caused by shrinkage or too much winding tension eventually causes deformation. It is identifiable by the pack of tape or film showing radial lines emanating out from the hub of the spool like spokes.

Sticky Shed Syndrome (SSS): Sticky shed is a problem unique to magnetic tape; it is caused by the chemical breakdown of the magnetic tape binder and/or backing layer of the tape. As the binder/backing absorb moisture from the surroundings, they become sticky and often shed brown residue to equipment. During playback the tape may squeal and bind, which can damage both tapes and equipment. This process is also referred to as binder hydrolysis.

Track Layout: Refers to the arrangement of recorded information on magnetic tapes. Tracks are either linear (running the length of the tape), or segmented either diagonally or perpendicularly across the tape. There are many variations within each technique, and some formats use a combination of techniques.

Vinegar Syndrome (magnetic media): Characteristic of the breakdown of the acetate tape binding and/or backing layer, resulting in the smell of vinegar (acetic acid). The tape may become brittle and difficult to handle.